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Abstract:

A photographing system includes: a photographing section photographing a
subject to acquire a frame image including a subject image; and a
matching section repeats image search through pattern matching between a
template image and a subject image while sequentially changing a size
ratio of the template image to the subject image, and obtains one or more
size ratios at which patterns match each other, in a certain order of
image search, and holds a size ratio having a largest value among such
obtained size ratios as a first size ratio, and thereafter performs image
search in a manner that pattern matching is performed at a first
frequency in a range of a size ratio equal to or larger than the first
size ratio, and is performed at a frequency lower than the first
frequency in a range of a size ratio smaller than the first size ratio.

Claims:

1. A photographing system comprising: a photographing section
photographing a subject to acquire a frame image including a subject
image; and a matching section changing size of one or both of the subject
image and a beforehand prepared template image to change a size ratio of
the template image to the subject image, and performing pattern matching
between the subject image and the template image, size of one or both of
the subject image and the template image being changed, for each of size
ratios, wherein the matching section repeats image search through pattern
matching while sequentially changing the size ratio, and obtains one or
more size ratios at which patterns match each other, in a certain order
of image search, and holds, as a first size ratio, a size ratio having a
largest value among such obtained size ratios, and thereafter performs
image search in a manner that pattern matching is performed at a first
frequency in a range of a size ratio equal to or larger than the first
size ratio, and is performed at a frequency lower than the first
frequency in a range of a size ratio smaller than the first size ratio.

2. The photographing system according to claim 1, wherein the matching
section holds, as a second size ratio, a size ratio having a smallest
value among the obtained size ratios in the certain order of image
search, and thereafter performs image search in a manner that pattern
matching is performed at a second frequency lower than the first
frequency in a range of a size ratio smaller than the first size ratio
and equal to or larger than the second size ratio, and is performed at a
third frequency lower than the second frequency in a range of a size
ratio smaller than the second size ratio.

3. The photographing system according to claim 1, wherein the matching
section changes the size ratio to be gradually reduced in each piece of
image search.

4. The photographing system according to claim 1, wherein if the patterns
do not match each other in the range of the size ratio equal to or larger
than the first size ratio in any image search after the image search in
which the first size ratio is obtained, the matching section performs
pattern matching across all size ratios in subsequent image search.

5. The photographing system according to claim 1, wherein the matching
section performs pattern matching through scanning the entire area of the
frame image while shifting a region as a matching object.

6. The photographing system according to claim 2, wherein the frame image
is divided into a plurality of regions, and the matching section sets the
first size ratio and the second size ratio for each of the divided
regions to set frequency of pattern matching for image search.

7. The photographing system according to claim 6, wherein the matching
section performs pattern matching through scanning the entire area of the
frame image while shifting a region as a matching object in a range of a
size ratio equal to or larger than a largest value among values of first
size ratios in the regions of the frame image.

8. The photographing system according to claim 6, further comprising a
motion detection section performing motion detection based on frame
difference between the plurality of frame images acquired at time points
different from one another, wherein the matching section corrects each of
the first and second size ratios for each of the regions of the frame
image based on a result of the motion detection.

9. The photographing system according to claim 2, wherein the matching
section acquires information on a relevant subject, based on the subject
image, and corrects each of the first and second size ratios based on the
information.

10. The photographing system according to claim 2, wherein the first size
ratio corresponds to a distance between the photographing section and a
subject nearest the photographing section, and the second size ratio
corresponds to a distance between the photographing section and a subject
most distant from the photographing section.

11. The photographing system according to claim 1, wherein the matching
section changes the size ratio by changing size of the frame image.

12. The photographing system according to claim 1, wherein the matching
section changes the size ratio by changing size of the template image.

13. The photographing system according to claim 1, wherein the subject is
a face.

14. A pattern detection system, comprising a matching section changing
size of one or both of a frame image including a subject image and a
beforehand prepared template image to change a size ratio of the template
image to the subject image, and performing pattern matching between the
subject image and the template image, size of one or both of the subject
image and the template image being changed, for each of size ratios,
wherein the matching section repeats image search through pattern
matching while sequentially changing the size ratio, and obtains one or
more size ratios at which patterns match each other, in a certain order
of image search, and holds, as a first size ratio, a size ratio having a
largest value among such obtained size ratios, and thereafter performs
image search in a manner that pattern matching is performed at a first
frequency in a range of a size ratio equal to or larger than the first
size ratio, and is performed at a frequency lower than the first
frequency in a range of a size ratio smaller than the first size ratio.

15. An electronic unit including a photographing system and a control
section performing operation control using the photographing system, the
photographing system comprising: a photographing section photographing a
subject to acquire a frame image including a subject image; and a
matching section changing size of one or both of the subject image and a
beforehand prepared template image to change a size ratio of the template
image to the subject image, and performing pattern matching between the
subject image and the template image, size of one or both of the subject
image and the template image being changed, for each of size ratios,
wherein the matching section repeats image search through pattern
matching while sequentially changing the size ratio, and obtains one or
more size ratios at which patterns match each other, in a certain order
of image search, and holds, as a first size ratio, a size ratio having a
largest value among such obtained size ratios, and thereafter performs
image search in a manner that pattern matching is performed at a first
frequency in a range of a size ratio equal to or larger than the first
size ratio, and performed at a frequency lower than the first frequency
in a range of a size ratio smaller than the first size ratio.

Description:

BACKGROUND

[0001] The present disclosure relates to a photographing system having a
pattern detection function, a pattern detection system used for the
photographing system, and an electronic unit including the photographing
system.

[0002] Recently, a photographing system such as a camera has been mounted
in various electronic units. An image pickup device configuring the
photographing system has been progressively reduced in size as typified
by a CMOS image sensor. Such a photographing system is used not only for
a stationary electronic unit, but also for a portable electronic unit.

[0003] In the electronic units, the photographing system photographs an
image that is used not only as a photograph but also for various
applications. Examples of the applications include a system that
recognizes a user face based on an image photographed by the
photographing system. For example, Japanese Unexamined Patent Application
Publication No. 2006-208558 discloses a camera that uses a result of face
detection to reduce a photographing interval for continuous
photographing.

SUMMARY

[0004] The face detection process detects a face from an image
photographed by the photographing system through, for example, pattern
detection. This may result in an increase in process time.

[0005] It is desirable to provide a photographing system, a pattern
detection system, and an electronic unit, each of which allows process
time to be reduced.

[0006] According to an embodiment of the present disclosure, there is
provided a photographing system including: a photographing section
photographing a subject to acquire a frame image including a subject
image; and a matching section changing size of one or both of the subject
image and a beforehand prepared template image to change a size ratio of
the template image to the subject image, and performing pattern matching
between the subject image and the template image, size of one or both of
the subject image and the template image being changed, for each of size
ratios. The matching section repeats image search through pattern
matching while sequentially changing the size ratio, and obtains one or
more size ratios at which patterns match each other, in a certain order
of image search, and holds, as a first size ratio, a size ratio having a
largest value among such obtained size ratios, and thereafter performs
image search in a manner that pattern matching is performed at a first
frequency in a range of a size ratio equal to or larger than the first
size ratio, and is performed at a frequency lower than the first
frequency in a range of a size ratio smaller than the first size ratio.

[0007] According to an embodiment of the present disclosure, there is
provided a pattern detection system including a matching section changing
size of one or both of a frame image including a subject image and a
beforehand prepared template image to change a size ratio of the template
image to the subject image, and performing pattern matching between the
subject image and the template image, size of one or both of the subject
image and the template image being changed, for each of size ratios. The
matching section repeats image search through pattern matching while
sequentially changing the size ratio, and obtains one or more size ratios
at which patterns match each other, in a certain order of image search,
and holds, as a first size ratio, a size ratio having a largest value
among such obtained size ratios, and thereafter performs image search in
a manner that pattern matching is performed at a first frequency in a
range of a size ratio equal to or larger than the first size ratio, and
is performed at a frequency lower than the first frequency in a range of
a size ratio smaller than the first size ratio.

[0008] According to an embodiment of the present disclosure, there is
provided an electronic unit including a photographing system and a
control section performing operation control using the photographing
system. The photographing system includes: a photographing section
photographing a subject to acquire a frame image including a subject
image; and a matching section changing size of one or both of the subject
image and a beforehand prepared template image to change a size ratio of
the template image to the subject image, and performing pattern matching
between the subject image and the template image, size of one or both of
the subject image and the template image being changed, for each of size
ratios. The matching section repeats image search through pattern
matching while sequentially changing the size ratio, and obtains one or
more size ratios at which patterns match each other, in a certain order
of image search, and holds, as a first size ratio, a size ratio having a
largest value among such obtained size ratios, and thereafter performs
image search in a manner that pattern matching is performed at a first
frequency in a range of a size ratio equal to or larger than the first
size ratio, and performed at a frequency lower than the first frequency
in a range of a size ratio smaller than the first size ratio. Examples of
the electronic unit include a television apparatus, a digital camera, and
a video camcorder.

[0009] In the photographing system, the pattern detection system, and the
electronic unit according to the embodiments of the disclosure, image
search is performed through pattern matching while a size ratio is
sequentially changed. In that operation, a size ratio at which patterns
match each other is obtained in a certain order of image search, and a
size ratio having a largest value among such obtained size ratios is held
as a first size ratio. Thereafter, the image search is performed such
that pattern matching is performed at a first frequency in a range of a
size ratio equal to or larger than the first size ratio, and performed at
a frequency lower than the first frequency in a range of a size ratio
smaller than the first size ratio.

[0010] According to the photographing system, the pattern detection
system, and the electronic unit according to the embodiments of the
disclosure, a first size ratio is obtained, and thereafter pattern
matching is performed at a first frequency in a range of a size ratio
equal to or larger than the first size ratio, and performed at a
frequency lower than the first frequency in a range of a size ratio
smaller than the first size ratio, thus achieving a reduction in process
time.

[0011] It is to be understood that both the foregoing general description
and the following detailed description are exemplary, and are intended to
provide further explanation of the technology as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings are included to provide a further
understanding of the disclosure, and are incorporated in and constitute a
part of this specification. The drawings illustrate embodiments and,
together with the specification, serve to explain the principles of the
technology.

[0013] FIG. 1 is a block diagram illustrating an exemplary configuration
of a display according to a first embodiment of the disclosure.

[0014]FIG. 2 is a block diagram illustrating an exemplary configuration
of a display drive section illustrated in FIG. 1.

[0035] FIG. 23 is another explanatory diagram illustrating the operation
example of the face detection section illustrated in FIG. 21.

[0036] FIGS. 24A and 24B are each another explanatory diagram illustrating
the operation example of the face detection section illustrated in FIG.
21.

[0037] FIG. 25 is another explanatory diagram illustrating the operation
example of the face detection section illustrated in FIG. 21.

[0038]FIG. 26 is a block diagram illustrating an exemplary configuration
of a display according to a modification of the second embodiment.

DETAILED DESCRIPTION OF EMBODIMENT

[0039] Hereinafter, embodiments of the present disclosure will be
described in detail with reference to the accompanying drawings. It is to
be noted that description is made in the following order.

[0040] 1. First Embodiment

[0041] 2. Second Embodiment

1. First Embodiment

Configuration Example

Overall Configuration Example

[0042] FIG. 1 illustrates an exemplary configuration of a display 1
according to a first embodiment. The display 1 detects a viewer viewing a
screen, and controls a backlight based on the detection result. It is to
be noted that a photographing system, a pattern detection system, and an
electronic unit according to embodiments of the disclosure are embodied
by the first embodiment, and therefore they are described together.

[0044] The control section 11 is configured of a circuit that controls the
display drive section 20 and the backlight drive section 16 based on an
image signal Sdisp. In detail, as described later, the control section 11
supplies an image signal Sdisp2 to the display drive section 20 to
control the display drive section 20, and supplies a control signal to
the backlight drive section 16 to control the backlight drive section 16.

[0045] The display drive section 20 drives the liquid crystal display
section 13 based on the image signal Sdisp2 supplied from the control
section 11. The liquid crystal display section 13 is configured of a
liquid crystal display device, and displays an image through modulating
light emitted from the backlight 17.

[0046]FIG. 2 illustrates an example of a block diagram including the
display drive section 20 and the liquid crystal display section 13. The
display drive section 20 includes a timing control section 21, a gate
driver 22, and a data driver 23. The timing control section 21 controls
drive timing of each of the gate driver 22 and the data driver 23, and
generates an image signal Sdisp3 based on the image signal Sdisp2
supplied from the control section 11, and supplies the image signal
Sdisp3 to the data driver 23. The gate driver 22 sequentially selects
pixels Pix in the liquid crystal display section 13 according to timing
control by the timing control section 21 for line sequential scan. The
data driver 23 supplies a pixel signal based on the image signal Sdisp3
to each of the pixels Pix in the liquid crystal display section 13.

[0047] The liquid crystal display section 13 includes a liquid crystal
material enclosed between two transparent substrates formed of, for
example, glass. A transparent electrode formed of, for example, indium
tin oxide (ITO) is provided on a surface of each of the transparent
substrates, the surface facing the liquid crystal material, and
configures the pixels Pix together with the liquid crystal material. The
liquid crystal display section 13 includes the pixels Pix arranged in a
matrix as illustrated in FIG. 2.

[0048] FIG. 3 illustrates an example of a circuit diagram of each pixel
Pix. The pixel Pix includes a thin film transistor (TFT) device Tr, a
liquid crystal device LC, and a holding capacitor Cs. The TFT device Tr
is configured of, for example, a metal oxide semiconductor-field effect
transistor (MOS-TFT), of which the gate is connected to a gate line GCL,
the source is connected to a data line SGL, and the drain is connected to
one end of the liquid crystal device LC and to one end of the holding
capacitor Cs. One end of the liquid crystal device LC is connected to the
drain of the TFT device Tr, and the other end thereof is grounded. One
end of the holding capacitor Cs is connected to the drain of the TFT
device Tr, and the other end thereof is connected to a holding
capacitance line CSL. The gate line GCL is connected to the gate driver
22, and the data line SGL is connected to the data driver 23.

[0049] The photographing section 14 photographs a viewer viewing the
screen of the display 1, and supplies a photographed image Pic to the
face detection section 30. The photographing section 14 performs
photographing, for example, ten times per second, and supplies such
photographed images Pic to the face detection section 30. The face
detection section 30 detects the face of the viewer based on the
photographed images Pic. Specifically, the face detection section 30
checks whether or not a viewer viewing the screen of the display 1
exists. Then, the face detection section 30 supplies a face detection
signal Sdet indicating information on whether or not such a viewer exists
to the backlight drive section 16.

[0050] The backlight drive section 16 drives the backlight based on the
control signal supplied from the control section 11 and the face
detection signal Sdet supplied from the face detection section 30. In
that operation, the backlight drive section 16 drives the backlight 17
based on the face detection signal Sdet such that if a viewer viewing the
screen of the display 1 exists, the backlight 17 is turned on, and if
such a viewer does not exist, the backlight 17 is turned off. In this
way, the display 1 achieves a reduction in power consumption through
controlling light emission of the backlight 17 depending on presence or
absence of the viewer.

[0051] The backlight 17 emits light based on the drive signal supplied
from the backlight drive section 16, and applies the light to the liquid
crystal display section 13. For example, the backlight 17 is configured
of a light emitting diode (LED). It is to be noted that the backlight 17
may be configured of, for example, a cold cathode fluorescent lamp (CCFL)
without limitation.

(Photographing Section 14 and Face Detection Section 30)

[0052] The photographing section 14 and the face detection section 30 are
now described in detail.

[0053] FIGS. 4A and 4B illustrate operation of the photographing section
14, where FIG. 4A illustrates an example of a position of each viewer
viewing the display 1, and FIG. 4B illustrates an example of a
photographed image Pic.

[0054] The example illustrated in FIG. 4A illustrates a case where three
viewers UA, UB, and UC view the display 1. In detail, the viewer UA is at
a position near the screen on the left side as viewed from the display 1,
the viewer UB is at a position slightly distant from the screen slightly
on the right side as viewed therefrom, and the viewer UC is at a position
distant from the screen on the right side as viewed therefrom, each
viewer viewing the screen of the display 1. A distance d from the display
1 is set in correspondence to a layer number LN (described later), as
described later. The photographing section 14 photographs these viewers
to acquire a photographed image Pic as illustrated in FIG. 4B. In the
photographed image Pic, a viewer at a position nearer the display 1 is
imaged larger. Specifically, in the photographed image Pic, the viewer UA
viewing at a position nearest the display 1 is imaged largest, the viewer
UB viewing at a position second-nearest the display 1 is imaged
second-largest, and the viewer UC viewing at a position most distant from
the display 1 is imaged smallest.

[0055] The face detection section 30 checks whether or not a viewer exists
based on the photographed image Pic. In that operation, if the face
detection section 30 detects the face of a viewer, the face detection
section 30 obtains a distance d between the viewer and the display 1. As
illustrated in FIG. 1, the face detection section 30 includes an image
resizing section 31, a template image supply section 32, a pattern
comparison section 33, a processing section 34, and a pattern comparison
control section 35.

[0056] The image resizing section 31 reduces the size of the photographed
image Pic supplied from the photographing section 14 based on an
instruction from the pattern comparison control section 35, and thus
resizes the photographed image Pic to form a photographed image Pic2. The
template image supply section 32 supplies a template image Ptemp
indicating a human face to the pattern comparison section 33. The pattern
comparison section 33 detects a human face within the photographed image
Pic2 through pattern comparison between the photographed image Pic2
supplied from the image resizing section 31 and the template image Ptemp
supplied from the template image supply section 32.

[0057] FIG. 5 illustrates a size reduction process of the photographed
image Pic by the image resizing section 31. As illustrated in FIG. 5, the
image resizing section 31 sequentially forms a plurality of (in this
exemplary case, ten) photographed images Pic2 through size reduction of
the photographed image Pic supplied from the photographing section 14.
Each photographed image Pic2 is assigned a layer number LN (0 to 9)
depending on corresponding rate R of size reduction. The rate R indicates
a ratio of size of a photographed image Pic2 to size of a photographed
image Pic. Specifically, in this exemplary case, the layer number LN of 0
corresponds to a rate R of 100%, and as the layer number LN increases,
corresponding rate R decreases.

[0058] The image resizing section 31 reduces size of a photographed image
Pic2 at a corresponding rate R based on information of the layer number
LN supplied from the pattern comparison control section 35, as described
later. In detail, if the image resizing section 31 receives an
instruction to form an image corresponding to the layer number LN of 0,
the image resizing section 31 outputs the photographed image Pic as the
photographed image Pic2 without size reduction. If the image resizing
section 31 receives an instruction to form images corresponding to layer
numbers LN of 1 to 9, the image resizing section 31 reduces the size of a
photographed image Pic at a rate R corresponding to each of the layer
numbers LN, and outputs such size-reduced photographed images Pic as the
photographed images Pic2.

[0059] In this exemplary case, the image resizing section 31 allows the
rate R to vary in ten stages through setting the layer number LN in ten
stages, 0 to 9. This, however, is not limitative. Alternatively, for
example, the image resizing section 31 may set the layer number LN in
nine stages or less or in eleven stages or more to allow the rate R to
vary correspondingly.

[0060] FIGS. 6A and 6B each illustrate an operation example of pattern
comparison by the pattern comparison section 33, where FIG. 6A
illustrates an operation example in the case of using a photographed
image Pic2 formed through size reduction at a rate R corresponding to the
layer number LN of 7, and FIG. 6B illustrates an operation example in the
case of using a photographed image Pic2 formed through size reduction at
a rate R corresponding to the layer number LN of 5.

[0061] The pattern comparison section 33 performs pattern comparison
between a photographed image Pic2 and a template image Ptemp. In that
operation, the pattern comparison section 33 checks whether or not a
pattern similar to the template image Ptemp exists within the
photographed image Pic2. In detail, as illustrated in FIGS. 6A and 6B,
while the pattern comparison section 33 gradually shifts a region to be
compared Rcomp having the same size as that of the template image Ptemp
in horizontal and vertical directions within the photographed image Pic2
to scan the photographed image Pic2, the pattern comparison section 33
performs pattern comparison between a portion of the photographed image
Pic2 in the region to be compared Rcomp and the template image Ptemp. In
the case where the template image Ptemp is configured of, for example, 20
by 20 pixels, a shifting distance of the region to be compared Rcomp is
set to a distance corresponding to two pixels, for example.

[0062] The image resizing section 31 forms the photographed images Pic2
through size reduction of the photographed image Pic at a rate R
corresponding to each of the various layer numbers LN, and supplies the
photographed images Pic2 to the pattern comparison section 33. The
pattern comparison section 33 performs pattern comparison for a
photographed image Pic2 corresponding to each layer number LN. For
example, in this exemplary case, in the case where a photographed image
Pic2 corresponding to a layer number LN of 7 is supplied, the pattern
comparison section 33 detects the face of the viewer UA viewing the
screen of the display 1 at a position near the display 1 through scanning
the photographed image Pic2 as illustrated in FIG. 6A. In the case where
a photographed image Pic2 corresponding to a layer number LN of 5 is
supplied, the pattern comparison section 33 detects the face of the
viewer UB viewing the screen of the display 1 at a position slightly
distant from the display 1 through scanning the photographed image Pic2
as illustrated in FIG. 6B. In other words, the face detection section 30
detects viewers at various distances d from the display 1 through pattern
comparison using the photographed images Pic2 corresponding to a
plurality of layer numbers LN.

[0063] In this way, the face detection section 30 obtains a distance d
from the display 1 to a viewer based on the layer number LN associated
with the photographed image Pic2 in which the face of the viewer is
detected. Specifically, the face detection section 30 detects the viewer
UA at a distance d corresponding to the layer number LN of 7 from the
display 1 and the viewer UB at a distance d corresponding to the layer
number LN of 5 from the display 1. As illustrated in FIG. 4A, the layer
number LN and the distance d are in a relationship where the distance d
from the display 1 is smaller/larger with a larger/smaller layer number
LN.

[0064] The pattern comparison section 33 supplies a result of face
detection performed in this way to the processing section 34. In detail,
the pattern comparison section 33 supplies information of the layer
number LN corresponding to a photographed image Pic2 in which the face of
a viewer is detected, the coordinates of the face, the number of detected
faces, and the like to the processing section 34.

[0065] In FIG. 1, the processing section 34 determines whether or not a
viewer viewing the display 1 exists, based on the result of face
detection by the pattern comparison section 33, and informs presence or
absence of the viewer of the backlight drive section 16. In addition, as
described later, the processing section 34 has a function of obtaining a
distance d from the display 1 to each detected viewer, and informing the
layer number LN corresponding to a viewer at a smallest distance d from
the display 1 as a layer threshold TH1 of the pattern comparison control
section 35, and informing the layer number LN corresponding to a viewer
at a largest distance d from the display 1 as a layer threshold TH2 of
the pattern comparison control section 35.

[0066] The pattern comparison control section 35 controls each operation
of the image resizing section 31 and the pattern comparison section 33.
The pattern comparison control section 35 includes a memory 36. The
memory 36 stores information of each of the layer thresholds TH1 and TH2
therein.

[0067] The pattern comparison control section 35 controls the image
resizing section 31 and the pattern comparison section 33 to perform
sequential face detection from a region near the display 1 to a region
distant from that. In detail, the pattern comparison control section 35
instructs the image resizing section 31 to decrease the layer number LN
in order from 9. The image resizing section 31 forms the photographed
images Pic2 while sequentially increasing the rate R for size reduction
of the photographed image Pic according to that instruction. Then, the
pattern comparison control section 35 instructs the pattern comparison
section 33 to perform pattern comparison for each of the photographed
images Pic2 supplied from the image resizing section 31.

[0068] In that operation, the pattern comparison control section 35
controls the image resizing section 31 and the pattern comparison section
33 to perform face detection at a relatively high frequency across the
blocks from the display 1 to a position of the viewer nearest the display
1, and at a relatively low frequency across the blocks behind the
position. In detail, as described later, the pattern comparison control
section 35 controls the image resizing section 31 and the pattern
comparison section 33 to perform face detection at a high frequency
(high-frequency detection M1) in the case of a layer number LN equal to
or larger than the layer threshold TH1, at a middle frequency
(middle-frequency detection M2) in the case of a layer number LN smaller
than the layer threshold TH1 and equal to or larger than the layer
threshold TH2, and at a low frequency (low-frequency detection M3) in the
case of a layer number LN smaller than the layer threshold TH2.

[0069] According to such a configuration, the face detection section 30
searches a viewer viewing the display 1 through sequential face detection
from a region near the display 1 to a region distant from that. In that
operation, the face detection section 30 checks whether one or more
viewers view the screen of the display 1 in a short process time through
face detection at a frequency that varies depending on the distance d
from the display 1.

[0070] The photographed image Pic corresponds to a specific example of
"frame image" of the disclosure. The face detection section 30
corresponds to a specific example of "matching section" of the
disclosure. The layer threshold TH1 corresponds to a specific example of
"first size ratio" of the disclosure. The layer threshold TH2 corresponds
to a specific example of "second size ratio" of the disclosure.

[Operation and Function]

[0071] The operation and the function of the display 1 according to the
first embodiment are now described.

(Outline of Overall Operation)

[0072] First, an outline of overall operation of the display 1 is
described with reference to FIG. 1. The control section 11 controls the
display drive section 20 and the backlight drive section 16. The display
drive section 20 drives the liquid crystal display section 13 based on
the image signal Sdisp2 supplied from the control section 11. The liquid
crystal display section 13 performs display through modulating light
emitted from the backlight 17. The photographing section 14 photographs a
viewer viewing the screen of the display 1. The face detection section 30
detects the face of the viewer based on a photographed image Pic
photographed by the photographing section 14, and outputs presence or
absence of a detected face as a face detection signal Sdet. In that
operation, the face detection section 30 operates to perform face
detection at a relatively high frequency across the blocks from the
display 1 to a position of a viewer nearest the display 1, and at a
relatively low frequency across the blocks behind the position. The
backlight drive section 16 drives the backlight 17 based on the control
signal supplied from the control section 11 and the face detection signal
Sdet supplied from the face detection section 30. In that operation, the
backlight drive section 16 drives the backlight 17 based on the face
detection signal Sdet such that if a viewer viewing the screen of the
display 1 exists, the backlight 17 is turned on, and if such a viewer
does not exist, the backlight 17 is turned off. The backlight 17 emits
light based on the drive signal supplied from the backlight drive section
16, and applies the light to the liquid crystal display section 13.

(Detailed Operation of Face Detection Section 30)

[0073] Operation of the face detection section 30 is now described. The
face detection section 30 performs face detection at a relatively high
frequency across the blocks from the display 1 to a position of a viewer
nearest the display 1, and at a relatively low frequency across the
blocks behind the position. Specifically, the face detection section 30
sequentially performs face detection from a region near the display 1 to
a region distant from that while sequentially decreasing the layer number
LN. In that operation, the face detection section 30 performs face
detection at a high frequency (high-frequency detection M1) in the case
of a layer number LN equal to or larger than the layer threshold TH1, at
a middle frequency (middle-frequency detection M2) in the case of a layer
number LN smaller than the layer threshold TH1 and equal to or larger
than the layer threshold TH2, and at a low frequency (low-frequency
detection M3) in the case of a layer number LN smaller than the layer
threshold TH2. Such operation of the face detection section 30 is
described in detail below with a specific example.

[0074] FIG. 7 illustrates the face detection operation by the face
detection section 30, where (A) and (B) each illustrate a case of one
viewer (cases C1 and C2), (C) illustrates a case of two viewers (case
C3), and (D) illustrates a case of three viewers (case C4). (A) of FIG. 7
illustrates a case where one viewer is at a position near the display 1
(case C1), and (B) thereof illustrates a case where one viewer is at a
position distant from the display 1 (case C2). In FIG. 7, the horizontal
axis indicates a distance d from the display 1. In other words, the
display 1 is located at the right end of FIG. 7, and the distance d is
larger at a position closer to the left end thereof.

[0075] In the case of one viewer (cases C1 and C2), as illustrated in (A)
and (B) of FIG. 7, the face detection section 30 performs face detection
through the high-frequency detection M1 across the blocks from the
display 1 to the viewer, and performs face detection through the
low-frequency detection M3 across the blocks more distant from the
display than the viewer. In detail, as illustrated in (A) of FIG. 7, if a
viewer is at a position corresponding to the layer number LN of 7 (case
C1), the face detection section 30 performs face detection through the
high-frequency detection M1 across the blocks corresponding to the layer
numbers LN of 9 to 7, and performs face detection through the
low-frequency detection M3 across the blocks corresponding to the layer
numbers LN of 6 to 0. In other words, in the case C1, since the viewer is
at the position corresponding to the layer number LN of 7, both the layer
threshold TH1 and the layer threshold TH2 are set to "7". Consequently,
the face detection section 30 performs face detection through the
high-frequency detection M1 across the blocks corresponding to the layer
numbers LN of 9 to 7 which are each equal to or larger than the layer
threshold TH1 (=7). In addition, the face detection section 30 performs
face detection through the low-frequency detection M3 across the blocks
corresponding to the layer numbers LN of 6 to 0 which are each smaller
than the layer threshold TH2 (=7). It is to be noted that the
middle-frequency detection M2 is not performed in this exemplary case
since the layer thresholds TH1 and TH2 are equal to each other.

[0076] Similarly, if a viewer is at a position corresponding to the layer
number LN of 2 (case C2), as illustrated in (B) of FIG. 7, the face
detection section 30 performs face detection through the high-frequency
detection M1 across the blocks corresponding to the layer numbers LN of 9
to 2, and performs face detection through the low-frequency detection M3
across the blocks corresponding to the layer numbers LN of 1 and 0. In
other words, in the case C2, since the viewer is at the position
corresponding to the layer number LN of 2, both the layer threshold TH1
and the layer threshold TH2 are set to "2". Consequently, the face
detection section 30 performs face detection through the high-frequency
detection M1 across the blocks corresponding to the layer numbers LN of 9
to 2 which are each equal to or larger than the layer threshold TH1 (=2).
In addition, the face detection section 30 performs face detection
through the low-frequency detection M3 across the blocks corresponding to
the layer numbers LN of 1 and 0 which are each smaller than the layer
threshold TH2 (=2). It is to be noted that the middle-frequency detection
M2 is not performed in this exemplary case since the layer thresholds TH1
and TH2 are equal to each other.

[0077] In the case of two viewers (case C3), as illustrated in (C) of FIG.
7, the face detection section 30 performs face detection through the
high-frequency detection M1 across the blocks from the display 1 to a
first viewer near the display 1, performs face detection through the
middle-frequency detection M2 across the blocks from the first viewer to
a second viewer distant from the display 1, and performs face detection
through the low-frequency detection M3 across the blocks more distant
from the display 1 than the second viewer. In detail, as illustrated in
(C) of FIG. 7, if a viewer UA is at a position corresponding to the layer
number LN of 7, and if a viewer UC is at a position corresponding to the
layer number LN of 2, the face detection section 30 performs face
detection through the high-frequency detection M1 across the blocks
corresponding to the layer numbers LN of 9 to 7, performs face detection
through the middle-frequency detection M2 across the blocks corresponding
to the layer numbers LN of 6 to 2, and performs face detection through
the low-frequency detection M3 across the blocks corresponding to the
layer numbers LN of 1 and 0. In other words, in the case C3, since the
viewer UA is at the position corresponding to the layer number LN of 7,
and the viewer UC is at the position corresponding to the layer number LN
of 2, the layer threshold TH1 is set to "7", and the layer threshold TH2
is set to "2". Consequently, the face detection section 30 performs face
detection through the high-frequency detection M1 across the blocks
corresponding to the layer numbers LN of 9 to 7 which are each equal to
or larger than the layer threshold TH1 (=7). In addition, the face
detection section 30 performs face detection through the middle-frequency
detection M2 across the blocks corresponding to the layer numbers LN of 6
to 2 which are each smaller than the layer threshold TH1 (=7) and equal
to or larger than the layer threshold TH2 (=2). In addition, the face
detection section 30 performs face detection through the low-frequency
detection M3 across the blocks corresponding to the layer numbers LN of 1
and 0 which are each smaller than the layer threshold TH2 (=2).

[0078] In the case of three viewers (case C4), as illustrated in (D) of
FIG. 7, the face detection section 30 performs face detection through the
high-frequency detection M1 across the blocks from the display 1 to a
first viewer nearest the display 1, performs face detection through the
middle-frequency detection M2 across the blocks from the first viewer to
a third viewer most distant from the display, and performs face detection
through the low-frequency detection M3 across the blocks more distant
from the display than the third viewer. In other words, the detection
frequency varies only between the front and the back of a viewer nearest
the display 1 and between the front and the back of a viewer most distant
from the display 1, as in the case of two viewers (case C3).

[0079] In the case of four or more viewers, the face detection section 30
operates in the same way as in the case of three viewers (case C4).
Specifically, the face detection section 30 performs face detection
through the high-frequency detection M1 across the blocks from the
display 1 to a first viewer nearest the display 1, performs face
detection through the middle-frequency detection M2 across the blocks
from the first viewer to a last viewer most distant from the display, and
performs face detection through the low-frequency detection M3 across the
blocks more distant from the display than the last viewer.

[0080] Next, detailed description is made on search operation of a viewer
through sequential face detection from a region near the display 1 to a
region distant from that in some of the above cases. In the following
exemplary case, the middle-frequency detection M2 is performed at a
frequency that is one fifth of the frequency of the high-frequency
detection M1, and the low-frequency detection M3 is performed at a
frequency that is one tenth of the frequency of the high-frequency
detection M1. This, however, is not limitative. The detection frequency
in each mode may be determined in consideration of capability of hardware
and other factors.

[0081] FIG. 8 illustrates search operation in the case of one viewer. FIG.
8 exemplarily illustrates detailed operation in the case C1 illustrated
in (A) of FIG. 7. Specifically, the face detection section 30 performs
face detection through the high-frequency detection M1 across the blocks
corresponding to the layer numbers LN of 9 to 7, and performs face
detection through the low-frequency detection M3 across the blocks
corresponding to the layer numbers LN of 6 to 0. In detail, as
illustrated in FIG. 8, first, the face detection section 30 performs
search D0 across all the blocks corresponding to the layer numbers LN of
9 to 0. Then, the face detection section 30 performs search D1 to D9 only
across the blocks corresponding to the layer numbers LN of 9 to 7. The
face detection section 30 repeats these ten pieces of search D0 to D9 in
total. Consequently, the face detection (low-frequency detection M3) is
performed across the blocks corresponding to the layer numbers LN of 6 to
0 at a frequency that is one tenth of the frequency of the face detection
(high-frequency detection M1) across the blocks corresponding to the
layer numbers LN of 9 to 7.

[0082] FIG. 9 illustrates search operation in the case of three viewers.
FIG. 9 exemplarily illustrates detailed operation in the case C4
illustrated in (D) of FIG. 7. Specifically, the face detection section 30
performs face detection through the high-frequency detection M1 across
the blocks corresponding to the layer numbers LN of 9 to 7, performs face
detection through the middle-frequency detection M2 across the blocks
corresponding to the layer numbers LN of 6 to 2, and performs face
detection through the low-frequency detection M3 across the blocks
corresponding to the layer numbers LN of 1 and 0. In detail, as
illustrated in FIG. 9, first, the face detection section 30 performs
search D10 across all the blocks corresponding to the layer numbers LN of
9 to 0. Then, the face detection section 30 performs search D11 to D14
only across the blocks corresponding to the layer numbers LN of 9 to 7.
In addition, the face detection section 30 performs search D15 only
across the blocks corresponding to the layer numbers LN of 9 to 2. Then,
the face detection section 30 performs search D16 to D19 only across the
blocks corresponding to the layer numbers LN of 9 to 7. The face
detection section 30 repeats these ten pieces of search D10 to D19 in
total. Consequently, the face detection (middle-frequency detection M2)
is performed across the blocks corresponding to the layer numbers LN of 6
to 2 at a frequency that is one fifth of the frequency of the face
detection (high-frequency detection M1) across the blocks corresponding
to the layer numbers LN of 9 to 7, and the face detection (low-frequency
detection M3) is performed across the blocks corresponding to the layer
numbers LN of 1 and 0 at a frequency that is one tenth of the frequency
of the face detection (high-frequency detection M1) in the blocks
corresponding to the layer numbers LN of 9 to 7.

[0083] FIG. 11 illustrates search operation in the case of no viewer. In
this case, the face detection section 30 operates to repeat search
operation across all the blocks corresponding to the layer numbers LN of
9 to 0.

[0084] In this way, the face detection section 30 performs face detection
at a high frequency (high-frequency detection M1) in the case of a layer
number LN equal to or larger than the layer threshold TH1, at a middle
frequency (middle-frequency detection M2) in the case of a layer number
LN smaller than the layer threshold TH1 and equal to or larger than the
layer threshold TH2, and at a low frequency (low-frequency detection M3)
in the case of a layer number LN smaller than the layer threshold TH2. In
other words, the face detection section 30 performs face detection at a
relatively high frequency (high-frequency detection M1) for a viewer
nearest the display 1, and performs face detection at a relatively low
frequency (middle-frequency detection M2) for other viewers.
Consequently, the face detection section 30 checks whether one or more
viewers view the screen of the display 1 in a short process time. The
process time is now described with an exemplary case of three viewers
(case C4).

[0085] In the case of three viewers (case C4), as illustrated in FIG. 9,
each piece of search D11 to D14 involves search of blocks of three layers
corresponding to the layer numbers LN of 9 to 7. In other words, the
pattern comparison section 33 detects the viewer UA through face
detection within each of three photographed images Pic2 corresponding to
the layer numbers LN of 9 to 7. In addition, for example, search D15
involves search of blocks of eight layers corresponding to the layer
numbers LN of 9 to 2. Specifically, the pattern comparison section 33
detects the viewers UA, UB, and UC through face detection within each of
eight photographed images Pic2 corresponding to the layer numbers LN of 9
to 2. In this operation, the number of layers to be searched is smaller
in each piece of search D11 to D14 than in search D15, and therefore time
for search operation (search time) is short in each piece of search D11
to D14 compared with in search D15.

[0086] FIG. 10 illustrates search time. In FIG. 10, the horizontal axis
indicates the number of layers to be searched. As illustrated in FIG. 10,
search time abruptly increases with an increase in the number of layers
to be searched.

[0087] The reason for this is as follows. The face detection section 30
performs face detection while sequentially decreasing the layer number LN
in search operation. In the face detection, as illustrated in FIGS. 6A
and 6B, the pattern comparison section 33 compares a portion of a
photographed image Pic2 in a region to be compared Rcomp to a template
image Ptemp while gradually shifting the region to be compared Rcomp in
horizontal and vertical directions within the photographed image Pic2 to
scan the photographed image Pic2. Since the number of times of pattern
comparison within a photographed image Pic2 is in proportion to the
screen resolution of the photographed image Pic2 (total pixel number), a
photographed image Pic2 corresponding to a smaller layer number LN
(larger rate R) involves a larger number of times of pattern comparison.
Accordingly, if the number of layers to be searched increases, pattern
comparison is added within a photographed image Pic2 corresponding to a
smaller layer number LN, resulting in an abrupt increase in search time
rather than an increase in search time in proportion to an increase in
the number of layers to be searched.

[0088] As illustrated in FIG. 10, search time in each piece of search D11
to D14 illustrated in FIG. 9 is about one thirtieth of search time in
search D10 performed across ten layers. Consequently, the face detection
section 30 reduces search time compared with, for example, a case of
constant search across all the blocks corresponding to the layer numbers
LN of 9 to 0 without change of detection frequency.

[0089] A typical display does not necessarily incorporate hardware having
high performance. In such a display, therefore, the search D10 across all
the blocks corresponding to the layer numbers LN of 9 to 0 may need
search time in seconds, for example. Even in such a case, search time is
extremely reduced by decreasing the number of layers to be searched, for
example, as in each piece of search D11 to D14. In the case of long
search time, much time is taken for search operation for photographed
images Pic that are photographed by the photographing section 14 and
sequentially supplied. Hence, such sequential photographed images Pic may
be only partially searched. Even in such a case, a relatively large
number of photographed images Pic are allowed to be searched through
reducing search time as above.

[0090] In this way, the face detection section 30 performs face detection
at a high frequency (high-frequency detection M1) across the blocks from
the display 1 to a position of a viewer nearest the display 1. As a
result, the face detection section 30 checks whether one or more viewers
view the screen of the display 1 in a short process time. Consequently,
the display 1 checks presence or absence of a viewer at a high frequency.
As a result, for example, if a viewer looks down to start reading a
magazine, the display 1 immediately turns off the backlight 17. If the
viewer restarts viewing the screen of the display 1, the display 1
immediately detects a face of the viewer and turn on the backlight 17.

[0091] In addition, in the case of a plurality of viewers, the face
detection section 30 performs face detection at a slightly low frequency
(middle-frequency detection M2) across the blocks from the viewer nearest
the display 1 to the viewer most distant from the display 1. As a result,
the face detection section 30 detects all viewers in a reduced process
time. Consequently, the face detection section 30 may be used not only
for an application where a process is carried out based on the position
of the viewer nearest the display 1, but also for an application where a
process is carried out based on positions of all viewers as described
later.

[0092] Furthermore, the face detection section 30 performs face detection
at a low frequency (low-frequency detection M3) across the blocks behind
the viewer most distant from the display. As a result, for example, even
if a new viewer is added in the blocks, the viewer is detected.

[0093] Moreover, when a viewer is at a position a predetermined distance
away from the display 1, face detection of the viewer may by useless
depending on a placed site of the display 1. In detail, for example, in
the case where the display 1 is placed in a small room, even if face
detection is performed over a distance from the display 1 to a wall in
front of the display 1, no face is detected. Even in such a case, the
display 1 reduces frequency of face detection across the blocks behind
the viewer most distant from the display 1, leading to a reduction in
ratio of process time for such detection operation to the total process
time.

[0094] Operation of the face detection section 30 is now described with a
flowchart.

[0095] FIG. 12 illustrates a flowchart of search operation by the face
detection section 30. In FIG. 12, the minimum detection distance Dmin is
a variable for storing a distance d from the display 1 to a viewer
nearest the display 1, and the maximum detection distance Dmax is a
variable for storing a distance d from the display 1 to a viewer most
distant from the display 1.

[0096] The face detection section 30 sequentially performs face detection
from a region near the display 1 to a region distant from that, and then
acquires a layer number LN at which a face is detected, and sets the
frequency of face detection based on the layer number LN. This is
described in detail below.

[0097] First, the face detection section 30 sequentially performs face
detection from a region near the display 1 to a region distant from that
(step S2). In detail, the pattern comparison control section 35 instructs
the image resizing section 31 to decrease the layer number LN in order
from 9. The image resizing section 31 forms photographed images Pic2
while increasing the rate R for size reduction of a photographed image
Pic in order according to that instruction. Then, the pattern comparison
section 33 performs face detection through pattern comparison using the
photographed images Pic2 supplied from the image resizing section 31 and
a template image Ptemp. In that operation, the pattern comparison control
section 35 controls the image resizing section 31 and the pattern
comparison section 33 to perform face detection at a frequency based on
the layer thresholds TH1 and TH2 stored in the memory 36. Then, the face
detection section 30 determines whether a face is detected in the face
detection process (step S3). If the face detection section 30 determines
detection of a face, the process advances to step S4. If the face
detection section 30 does not determine detection of a face, the process
returns to step S2 for a next face detection process.

[0098] If the face detection section 30 determines detection of a face in
the face detection process of step S2, the processing section 34 of the
face detection section 30 acquires information of a layer number LN
associated with a photographed image Pic2 in which a face of a viewer is
detected, the number of detected faces (detection number), and the like
from the detection result in the face detection process (step S4).

[0099] Then, the processing section 34 of the face detection section 30
acquires a distance d (detection distance) from the display 1 to each
viewer, based on the layer number LN corresponding to the viewer acquired
in step S4 (step S5).

[0100] Then, the processing section 34 of the face detection section 30
updates the minimum detection distance Dmin and the maximum detection
distance Dmax (step S6). In detail, the processing section 34 sets a
distance d associated with the viewer nearest the display 1, among the
viewers, as the minimum detection distance Dmin, and sets a distance d
associated with the viewer most distant from the display 1 as the maximum
detection distance Dmax.

[0101] Then, the face detection section 30 updates each of the layer
thresholds TH1 and TH2 (step S7). In detail, first, the processing
section 34 obtains a layer number LN corresponding to the minimum
detection distance Dmin acquired in step S6, and supplies the layer
number LN as the layer threshold TH1 to the pattern comparison control
section 35. In addition, the processing section 34 obtains a layer number
LN corresponding to the maximum detection distance Dmax acquired in step
S6, and supplies the layer number LN as the layer threshold TH2 to the
pattern comparison control section 35. Then, the memory 36 in the pattern
comparison control section 35 stores the updated layer thresholds TH1 and
TH2 therein.

[0102] This is the end of flow of the search operation.

[0103] Thereafter, the face detection section 30 executes this flow in
subsequent search operation. In that operation, the face detection
process (step S2) is performed at a frequency based on the layer
thresholds TH1 and TH2 updated in step S7 of the previous search
operation. In this way, the face detection section 30 updates each of the
layer thresholds TH1 and TH2 at every search operation, and sets the
frequency of face detection based on the updated layer thresholds TH1 and
TH2.

[0104] It is to be noted that the face detection section 30 is desirably
configured to maintain the layer thresholds TH1 and TH2 even if the
display 1 is in a standby mode, for example. According to such a
configuration, when the display 1 is returned from the standby mode to an
operation mode, the face detection section 30 checks whether one or more
viewers view a screen in a short process time.

[0105] Next, description is made on operation of the face detection
section 30 in the case where a viewer viewing the screen of the display 1
moves.

[0106] FIGS. 13 and 14 illustrate search operation in the case of one
viewer, where FIG. 13 illustrates a case where the viewer moves closer to
the display 1, and FIG. 14 illustrates a case where the viewer moves away
from the display 1. In this exemplary case, it is assumed that the viewer
is initially at a position corresponding to the layer number LN of 7 as
in the case C1 ((A) of FIG. 7 and FIG. 8).

[0107] As illustrated in FIGS. 13 and 14, in the case where the viewer is
initially at the position corresponding to the layer number LN of 7, the
face detection section 30 performs search D0 to D6 as in the case
illustrated in FIG. 8.

[0108] As illustrated in FIG. 13, if the viewer moves closer to the
display 1 at timing t1, the face detection section 30 then searches
blocks corresponding to the layer numbers LN of 9 to 7 in subsequent
search D37, as in the search D1 to D6. In the search D37, the face
detection section 30 detects shift of the viewer from the position
corresponding to the layer number LN of 7 to a position corresponding to
the layer number LN of 8. Thus, the face detection section 30 searches
only blocks corresponding to the layer numbers LN of 9 and 8 in
subsequent search D38 or later. In other words, the face detection
section 30 operates to minimize the number of layers to be searched.
Consequently, the face detection section 30 checks whether one or more
viewers view the screen of the display 1 in a short process time.

[0109] As illustrated in FIG. 14, if the viewer moves away from the
display 1 at timing t2, the face detection section 30 then searches
blocks corresponding to the layer numbers LN of 9 to 7 in subsequent
search D47, as in the search D1 to D6. In the search D47, the face
detection section 30 detects absence of the viewer from the blocks
corresponding to the layer numbers LN 9 to 7. Thus, the face detection
section 30 searches all the blocks corresponding to the layer numbers LN
of 9 to 0 in subsequent search D50. In the search D50, the face detection
section 30 detects the viewer at a position corresponding to the layer
number LN of 6. Thus, the face detection section 30 searches blocks
corresponding to the layer numbers LN of 9 to 6 in subsequent search D51
or later. In this way, even if a viewer moves away from the display 1,
the face detection section 30 immediately detects the viewer and changes
blocks to be searched depending on the position of the moved viewer.

[0110] FIGS. 15 and 16 each illustrate search operation in the case of
three viewers, where FIG. 15 illustrates a case where a viewer nearest
the display 1 among the three viewers moves closer to the display 1, and
FIG. 16 illustrates a case where the viewer nearest the display 1 moves
away from the display 1. In this exemplary case, it is assumed that the
respective three viewers are initially at positions corresponding to the
layer numbers LN of 7, 5, and 2 as in the case C4 ((D) of FIG. 7 and FIG.
9).

[0111] As illustrated in FIGS. 15 and 16, in the case where the viewer UA
nearest the display 1 is initially at a position corresponding to the
layer number LN of 7, the face detection section 30 performs search D10
to D16 as in the case illustrated in FIG. 9.

[0112] As illustrated in FIG. 15, if the viewer UA moves closer to the
display 1 at timing t3, the face detection section 30 then searches
blocks corresponding to the layer numbers LN of 9 to 7 in subsequent
search D67, as in the search D11 to D14 and D16. In the search D67, the
face detection section 30 detects shift of the viewer from the position
corresponding to the layer number LN of 7 to a position corresponding to
the layer number LN of 8. Thus, the face detection section 30 searches
only blocks corresponding to the layer numbers LN of 9 and 8 in
subsequent search D68 or later. In other words, the face detection
section 30 operates to minimize the number of layers to be searched.
Consequently, the face detection section 30 checks whether one or more
viewers view the screen of the display 1 in a short process time.

[0113] As illustrated in FIG. 16, if the viewer UA moves away from the
display 1 at timing t4, the face detection section 30 then searches
blocks corresponding to the layer numbers LN of 9 to 7 in subsequent
search D77, as in the search D11 to D14 and D16. In the search D77, the
face detection section 30 detects absence of the viewer UA from the
blocks corresponding to the layer numbers LN 9 to 7. Thus, the face
detection section 30 searches all the blocks corresponding to the layer
numbers LN of 9 to 0 in subsequent search D80. In the search D80, the
face detection section 30 detects the viewer UA at a position
corresponding to the layer number LN of 6. Thus, the face detection
section 30 searches blocks corresponding to the layer numbers LN of 9 to
6 in subsequent search D81 or later. In this way, even if a viewer moves
away from the display 1, the face detection section 30 immediately
detects the viewer and changes blocks to be searched depending on the
position of the moved viewer.

[0114] In this way, even if a viewer moves, the display 1 immediately
detects the viewer and changes blocks to be searched depending on the
position of the moved viewer.

EFFECTS

[0115] As described above, in the first embodiment, since face detection
is performed at a high frequency across the blocks from the display to
the position of the viewer nearest the display, whether one or more
viewers view the screen of the display is checked in a short process
time.

[0116] In addition, in the first embodiment, since face detection is
performed at a slightly low frequency across the blocks from the viewer
nearest the display to the viewer most distant from the display, all
viewers are detected with a reduced process time.

[0117] Furthermore, in the first embodiment, face detection is performed
at a low frequency across the blocks behind the viewer most distant from
the display. As a result, even if a new viewer is added in the blocks,
the viewer is detected, while the ratio of process time for face
detection operation across the blocks to the total process time is
reduced.

[Modification 1-1]

[0118] Although the backlight 17 is controlled to be turned on or off
based on a detection result by the face detection section 30 in the first
embodiment, this is not limitative. This is described in detail below.

[0119]FIG. 17 illustrates an exemplary configuration of a display 1B
according to modification 1-1. The display 1B changes an image or the
like displayed on the liquid crystal display section 13, based on a
detection result by the face detection section 30. In this exemplary
case, the display 1B has a function of notifying a viewer to move away
from the screen of the display 1B if the viewer is extremely close to the
screen.

[0120] The display 1B includes a face detection section 30B, a control
section 11B, and a backlight drive section 16B. The face detection
section 30B includes a processing section 34B. The processing section 34B
supplies a distance d from the display 1B to a viewer nearest the display
1B as a face detection signal Sdet2, based on a face detection result by
the pattern comparison section 33. The control section 11B processes an
image signal such that, if a distance between the display 1B and the
viewer is shorter than a predetermined distance, "get away from a
screen!" is shown in a form of, for example, on-screen display (OSD),
based on the face detection signal Sdet2 supplied from the processing
section 34B of the face detection section 30. The backlight drive section
16B drives the backlight 17 based on a control signal supplied from the
control section 11B.

[0121] According to such a configuration of the display 1B, if a viewer is
extremely close to the screen of the display 1B, a message is displayed
to prompt the viewer to get away from the screen. In that operation,
since the face detection section 30B performs face detection at a high
frequency (high-frequency detection M1) across the blocks from the
display 1B to a position of a viewer nearest the display 1B, the face
detection section 30B detects the viewer in a short process time, as in
the face detection section 30 according to the first embodiment.
Consequently, for example, even if a child suddenly gets close to the
screen, the display 1B immediately prompts the child to get away from the
screen. It is to be noted that, although a message is displayed to notify
a viewer of an event in the exemplary case, this is not limitative. For
example, sound may be used to notify a viewer of the event instead of or
in addition to that.

[Modification 1-2]

[0122] Although the liquid crystal display section 13 performs display
operation in the first embodiment, this is not limitative. Alternatively,
for example, an electro-luminescence (EL) display section 13C may perform
display operation, as illustrated in FIG. 18. In this case, for example,
the face detection section 30 may control the EL display section 13C to
perform black display in the case of no viewer.

[Modification 1-3]

[0123] Although the face detection section 30 performs size reduction of
the photographed image Pic to form the photographed image Pic2, and
performs face detection through pattern comparison between the
photographed image Pic2 and the template image Ptemp, this is not
limitative. This is described in detail below with an exemplary case.

[0124] FIG. 19 illustrates an exemplary configuration of a display 1D
according to modification 1-3. The display 1D includes a face detection
section 30D. The face detection section 30D includes an image resizing
section 37. The image resizing section 37 forms a template image Ptemp2
through scaling of the template image Ptemp supplied from the template
image supply section 32, and supplies the template image Ptemp2 to the
pattern comparison section 33.

[0125] According to this configuration, the face detection section 30D
generates the template image Ptemp2 through scaling of the template image
Ptemp, and performs face detection through pattern comparison between a
photographed image Pic and the template image Ptemp2.

[0126] FIGS. 20A and 20B each illustrate an operation example of pattern
comparison according to the modification 1-3, where FIG. 20A illustrates
an operation example in the case of using a template image Ptemp2 formed
through scaling at a first rate RD, and FIG. 20B illustrates an operation
example in the case of using another template image Ptemp2 formed through
scaling at a second rate RD.

[0127] The image resizing section 37 forms template images Ptemp2 through
scaling of the template image Ptemp at various rates RD according to an
instruction from the pattern comparison control section 35, and supplies
the template images Ptemp2 to the pattern comparison section 33. The
pattern comparison section 33 gradually shifts a region to be compared
Rcomp having the same size as that of each template image Ptemp2 in
horizontal and vertical directions to scan the photographed image Pic,
and concurrently performs pattern comparison between a portion of the
photographed image Pic in the region to be compared Rcomp and the
template image Ptemp2. Consequently, in the operation example illustrated
in FIG. 20A, the face detection section 30D detects a face of a viewer UA
viewing a screen at a position near the display 1D. In the operation
example illustrated in FIG. 20B, the face detection section 30D detects a
face of a viewer UB viewing the screen at a position slightly distant
from the display 1D. In this way, the face detection section 30D detects
viewers at various distances d from the display 1D.

[Modification 1-4]

[0128] In the first embodiment, as illustrated in steps S4 and S5 of FIG.
12, a distance d from a display to a viewer is obtained based on a layer
number LN at which the face of the viewer is detected. In that operation,
the viewer may be determined to be a child or an adult based on, for
example, a photographed image Pic so that the distance d is corrected
based on that determination result. Specifically, even if an adult face
and a child face are detected together in a photographed image Pict
associated with the same layer number LN, the child viewer is likely to
be actually at a position distant from the display compared with the
adult viewer in consideration that a child face is usually smaller than
an adult face. Accordingly, the distance d from the display to a viewer
is obtained while being corrected in consideration of a difference in
size between a child face and an adult face, so that information of a
distance associated with each viewer is more accurately obtained.

[Modification 1-5]

[0129] In the first embodiment, as illustrated in FIG. 12, a distance d
from a display to a viewer is obtained based on a layer number LN at
which the face of the viewer is detected, and the layer thresholds TH1
and TH2 are obtained based on the distance d. This, however, is not
limitative. Alternatively, for example, the layer thresholds TH1 and TH2
may be directly obtained from that layer number LN. In this case, for
example, among the layer numbers LN at which faces of viewers are
detected, a largest layer number LN may be set to the layer threshold
TH1, and a smallest layer number LN may be set to the layer threshold
TH2.

[Modification 1-6]

[0130] Although the middle-frequency detection M2 is performed at a
frequency that is one fifth of the frequency of the high-frequency
detection M1, and the low-frequency detection M3 is performed at a
frequency that is one tenth of the frequency of the high-frequency
detection M1 in the first embodiment, this is not limitative.
Alternatively, such frequencies may be designed to be dynamically
changed. For example, modification 1-6 is effective in the case where
another application is executed based on a detection result by the face
detection section 30. Specifically, during execution of the application,
if whether one or more viewers view a screen is desired to be exclusively
checked, the middle-frequency detection M2 may be performed at a lower
frequency. On the other hand, if the number of viewers is desired to be
determined, the middle-frequency detection M2 may be performed at a
higher frequency.

2. Second Embodiment

[0131] A display 2 according to a second embodiment is now described. The
second embodiment is configured such that a photographed image Pic is
divided into a plurality of regions, and frequency of face detection may
be changed for each of the divided regions. Here, description is made on
an exemplary case where a photographed image Pic is divided into two, or
right and left regions. It is to be noted that substantially the same
components as those of the display 1 according to the first embodiment
are designated by the same numerals, and description of them is
appropriately omitted.

[0132] FIG. 21 illustrates an exemplary configuration of a display 2
according to the second embodiment. The display 2 includes a face
detection section 40. The face detection section 40 includes a pattern
comparison control section 45. The pattern comparison control section 45
includes a memory 46 that stores four layer thresholds THL1, THL2, THR1,
and THR2 therein. The pattern comparison control section 45 controls the
image resizing section 31 and the pattern comparison section 33 to
perform sequential face detection from a region near the display 2 to a
region distant from that, as in the pattern comparison control section 35
according to the first embodiment. In that operation, the pattern
comparison control section 45 controls the image resizing section 31 and
the pattern comparison section 33 to perform face detection at a
frequency based on the layer thresholds THL1 and THL2 for an image at a
left half of the photographed image Pic, and perform face detection at a
frequency based on the layer thresholds THR1 and THR2 for an image at a
right half thereof.

[0133] FIGS. 22A and 22B illustrate an example of operation of the face
detection section 40, where FIG. 22A illustrates an example of positions
of viewers viewing the display 2, and FIG. 22B illustrates an example of
the photographed image Pic.

[0134] The photographing section 14 photographs viewers UA, UB, and UC
viewing the display 2 as illustrated in FIG. 22A to acquire a
photographed image Pic as illustrated in FIG. 22B, as in the case of the
first embodiment. The face detection section 40 performs face detection
while setting different frequencies for an image in a region PL at the
left half of the photographed image Pic and for an image in a region PR
at the right half thereof.

[0135] In detail, at the left side as viewed from the display 2, as
illustrated in FIG. 22A, the face detection section 40 performs face
detection through the high-frequency detection M1 across blocks
corresponding to the layer number LN of 9 to 7, and performs face
detection through the low-frequency detection M3 across blocks
corresponding to the layer number LN of 6 to 0. In other words, since the
viewer UA is at a position corresponding to the layer number LN of 7 at
the left side as viewed from the display 2, both the layer threshold THL1
and the layer threshold THL2 are set to "7". Thus, the face detection
section 40 performs face detection through the high-frequency detection
M1 across the blocks corresponding to the layer numbers LN of 9 to 7
which are each equal to or larger than the layer threshold THL1 (=7). In
addition, the face detection section 40 performs face detection through
the low-frequency detection M3 across the blocks corresponding to the
layer numbers LN of 6 to 0 which are each smaller than the layer
threshold THL2 (=2). It is to be noted that the middle-frequency
detection M2 is not performed in this exemplary case since the layer
thresholds THL1 and THL2 are equal to each other.

[0136] At the right side as viewed from the display 2, as illustrated in
FIG. 22A, the face detection section 40 performs face detection through
the high-frequency detection M1 across blocks corresponding to the layer
number LN of 9 to 5, performs face detection through the middle-frequency
detection M2 across blocks corresponding to the layer number LN of 4 to
2, and performs face detection through the low-frequency detection M3
across blocks corresponding to the layer number LN of 1 and 0. In other
words, at the right side as viewed from the display 2, since the viewer
UB is at a position corresponding to the layer number LN of 5, and the
viewer UC is at a position corresponding to the layer number LN of 2, the
layer threshold THR1 is set to "5", and the layer threshold THR2 is set
to "2". Thus, the face detection section 40 performs face detection
through the high-frequency detection M1 across the blocks corresponding
to the layer numbers LN of 9 to 5 which are each equal to or larger than
the layer threshold THR1 (=5). In addition, the face detection section 40
performs face detection through the middle-frequency detection M2 across
the blocks corresponding to the layer numbers LN of 4 to 2 which are each
smaller than the layer threshold THR1 (=5) and equal to or larger than
the layer threshold THR2 (=2). In addition, the face detection section 40
performs face detection through the low-frequency detection M3 across
blocks corresponding to the layer numbers LN of 1 and 0 which are each
smaller than the layer threshold THR2 (=2).

[0137] (A) of FIG. 23 illustrates search operation at the left side as
viewed from the display 2, and (B) of FIG. 23 illustrates search
operation at the right side as viewed from the display 2.

[0138] At the left side as viewed from the display 2, as illustrated in
(A) of FIG. 23, first, the face detection section 40 performs search DL0
across all the blocks corresponding to the layer numbers LN of 9 to 0.
Then, the face detection section 40 performs search DL1 to DL9 only
across the blocks corresponding to the layer numbers LN of 9 to 7. The
face detection section 40 repeats the ten pieces of search DL0 to DL9.
Consequently, the face detection (low-frequency detection M3) is
performed across the blocks corresponding to the layer numbers LN of 6 to
0 at a frequency that is one tenth of the frequency of the face detection
(high-frequency detection M1) across the blocks corresponding to the
layer numbers LN of 9 to 7.

[0139] At the right side as viewed from the display 2, as illustrated in
(B) of FIG. 23, first, the face detection section 40 performs search DR0
across all the blocks corresponding to the layer numbers LN of 9 to 0.
Then, the face detection section 40 performs search DR1 to DR4 only
across the blocks corresponding to the layer numbers LN of 9 to 5. In
addition, the face detection section 40 performs search DR5 only across
the blocks corresponding to the layer numbers LN of 9 to 2. Then, the
face detection section 40 performs search DR6 to DR9 only across the
blocks corresponding to the layer numbers LN of 9 to 5. The face
detection section 40 repeats these ten pieces of search DR0 to DR9.
Consequently, face detection (middle-frequency detection M2) is performed
across the blocks corresponding to the layer numbers LN of 4 to 2 at a
frequency that is one fifth of the frequency of the face detection
(high-frequency detection M1) across the blocks corresponding to the
layer numbers LN of 9 to 5, and face detection (low-frequency detection
M3) is performed across the blocks corresponding to the layer numbers LN
of 1 and 0 at a frequency that is one tenth of the frequency of the face
detection (high-frequency detection M1) across the blocks corresponding
to the layer numbers LN of 9 to 5.

[0140] As illustrated in FIG. 23, each piece of search DL0 to DL9 at the
left side as viewed from the display 2 is performed at timing
corresponding to timing of each piece of search DR0 to DR9 at the right
side as viewed from the display 2. This is described below with a
specific example.

[0141] FIGS. 24A and 24B illustrate an operation example of face detection
using a photographed image Pict associated with the layer number LN of 5,
where FIG. 24A illustrates face detection in the search DL0 and DR0, and
FIG. 24B illustrates face detection in the search DR1.

[0142] As illustrated in FIG. 23, both the search DL0 and the search DR0
involve face detection for the photographed image Pic2 associated with
the layer number LN of 5. Accordingly, in this case, as illustrated in
FIG. 24A, the face detection section 40 performs face detection through
scanning the entire photographed image Pic2.

[0143] On the other hand, for example, as illustrated in FIG. 23, only the
search DR1 between the search DL1 and the search DR1 involves face
detection for the photographed image Pic2 associated with the layer
number LN of 5. Accordingly, in this case, as illustrated in FIG. 24B,
the face detection section 40 performs face detection through scanning
only the right-half region PR of the photographed image Pic2.

[0144] FIG. 25 illustrates an operation example of face detection using a
photographed image Pic2 associated with the layer number LN of 7. This
operation example shows face detection involved in the search DL1 and
DR1. As illustrated in FIG. 23, both the search DL1 and the search DR1
involve face detection for the photographed image Pic2 associated with
the layer number LN of 7. Accordingly, in this case, as illustrated in
FIG. 25, the face detection section 40 performs face detection through
scanning the entire photographed image Pic2. Specifically, in this
example, the layer threshold THL1 is 7, and the layer threshold THR1 is
5. Hence, face detection is performed in both the left side and the right
side across the blocks corresponding to the layer numbers LN of 7 to 9
which are each equal to or larger than the largest value (7) of the layer
thresholds THL1 and THR1. Accordingly, the face detection section 40
performs face detection through scanning the entire photographed image
Pic2 across the blocks corresponding to the layer numbers LN of 7 to 9.

[0145] In this way, in the case where both left search and corresponding
right search involve face detection at a position corresponding to a
certain layer number LN, the face detection section 40 performs face
detection through scanning the entire photographed image Pic2. In
addition, in the case where one of left search and right search involves
face detection at a position corresponding to a certain layer number LN,
the face detection section 40 performs face detection through scanning
only a corresponding region in the photographed image Pic2.

[0146] As described above, in the second embodiment, a photographed image
is divided into a plurality of regions, and frequency of face detection
is set for each of the divided regions. Hence, frequency of face
detection is reduced for a region in which no face is expected to be
detected, thus achieving a short search time. Other effects are similar
to those in the first embodiment.

[Modification 2-1]

[0147] For example, the second embodiment may be modified such that a
region for face detection is limited by using motion detection. This is
described in detail below with an exemplary case.

[0148]FIG. 26 illustrates an exemplary configuration of a display 2B
according to modification 2-1. The display 2B includes a face detection
section 40B. The face detection section 40B includes a motion detection
section 47 and a pattern comparison control section 45B. The motion
detection section 47 performs motion detection using frame difference,
based on a series of photographed images Pic. Then, the motion detection
section 47 supplies information on a portion in which motion is detected,
in each photographed image Pic to the pattern comparison control section
45B. The pattern comparison control section 45B sets the frequency of
face detection for individual regions with reference to the information
supplied from the motion detection section 47. In detail, for example, a
person may not face the display 2B since he/she has just moved to the
front of the display 2B, and therefore the pattern comparison section 33
and the like have not recognized his/her face. The motion detection
section 47 detects such a person, and supplies information of the person
to the pattern comparison control section 45B. In other words, the person
may be a viewer of the display 2B soon. For example, the pattern
comparison control section 45B sets the layer thresholds THL1, THL2,
THR1, and THR2 based on the supplied information such that, when the
person faces the display 2B, the face of the person is detected at a high
frequency. Consequently, even if a new viewer is added, the display 2B
immediately performs face detection for the viewer.

[Modification 2-2]

[0149] Although a photographed image Pic is divided into, for example,
two, or right and left (horizontal) regions in the second embodiment,
this is not limitative. Alternatively, for example, the photographed
image Pic may be divided into three or more horizontal regions, or may be
divided into two or more vertical (perpendicular) regions. Alternatively,
these may be combined so that the photographed image Pic is divided into
a matrix.

[Modification 2-3]

[0150] For example, the modifications of the first embodiment may be
applied to the second embodiment.

[0151] While the present technology has been described with the
embodiments and the modifications hereinbefore, the technology may be
used for various applications. For example, the technology may be used
for gamma correction based on a position of a viewer nearest a display.
Specifically, for example, different types of gamma correction may be
performed between a case of the viewer at the front of the screen of the
display and a case of the viewer at a position slightly displaced from
the front. Alternatively, sound balance between right and left may be
adjusted based on a position of a viewer nearest a display.
Alternatively, for example, in the case where a display is a stereoscopic
display, parallax between a left-eye image and a right-eye image may be
adjusted based on a distance between the display and a viewer.
Alternatively, the technology may be used to control the directivity of a
microphone to be in a direction toward a speaker in a videoconference
system. Specifically, beam forming, which is one of microphone
characteristics, is dynamically changed to be in a direction toward a
speaker, so that voice of only a desired speaker is captured while
surrounding noise is reduced. In addition, the technology may be applied
to digital signage. In addition, for example, the various processes in
the applications may be performed not only based on the position of a
viewer nearest a display, but also based on a position of another viewer.

[0152] Although the embodiments and the modifications have been
exemplarily described with a display, the present technology is not
limited thereto, and the technology may be used for an application where
a position of a face is detected, and operation is performed following
the position. For example, the technology may be used for applications of
an air conditioner, a humidifier, various types of face care products,
and the like, where a position of a user face is followed, and air or
mist is fed to the position. In addition, although the technology is used
for the applications where operation is performed following a position of
a user face in the above exemplary case, the technology is not limited
thereto, and the technology may be used for an application where
operation is performed while a position of a user face is constantly
avoided.

[0153] In addition, although the face of a viewer has been detected in the
embodiments and the modifications, the technology is not limited thereto.
For example, a detection section having a configuration similar to that
of the face detection section 30 may be mounted in a motor vehicle to
detect another vehicle approaching. Consequently, for example, an
approaching vehicle is detected in a short process time.

[0154] It is to be noted that the technology may be configured as follows.

[0155] (1) A photographing system including:

[0156] a photographing section photographing a subject to acquire a frame
image including a subject image; and

[0157] a matching section changing size of one or both of the subject
image and a beforehand prepared template image to change a size ratio of
the template image to the subject image, and performing pattern matching
between the subject image and the template image, size of one or both of
the subject image and the template image being changed, for each of size
ratios,

[0158] wherein the matching section repeats image search through pattern
matching while sequentially changing the size ratio, and obtains one or
more size ratios at which patterns match each other, in a certain order
of image search, and holds, as a first size ratio, a size ratio having a
largest value among such obtained size ratios, and thereafter performs
image search in a manner that pattern matching is performed at a first
frequency in a range of a size ratio equal to or larger than the first
size ratio, and is performed at a frequency lower than the first
frequency in a range of a size ratio smaller than the first size ratio.

[0159] (2) The photographing system according to (1),

[0160] wherein the matching section holds, as a second size ratio, a size
ratio having a smallest value among the obtained size ratios in the
certain order of image search, and thereafter performs image search in a
manner that pattern matching is performed at a second frequency lower
than the first frequency in a range of a size ratio smaller than the
first size ratio and equal to or larger than the second size ratio, and
is performed at a third frequency lower than the second frequency in a
range of a size ratio smaller than the second size ratio.

[0161] (3) The photographing system according to (1) or (2), wherein the
matching section changes the size ratio to be gradually reduced in each
piece of image search.

[0162] (4) The photographing system according to any one of (1) to (3),
wherein if the patterns do not match each other in the range of the size
ratio equal to or larger than the first size ratio in any image search
after the image search in which the first size ratio is obtained, the
matching section performs pattern matching across all size ratios in
subsequent image search.

[0163] (5) The photographing system according to any one of (1) to (4),
wherein the matching section performs pattern matching through scanning
the entire area of the frame image while shifting a region as a matching
object.

[0164] (6) The photographing system according to (2), wherein the frame
image is divided into a plurality of regions, and the matching section
sets the first size ratio and the second size ratio for each of the
divided regions to set frequency of pattern matching for image search.

[0165] (7) The photographing system according to (6), wherein the matching
section performs pattern matching through scanning the entire area of the
frame image while shifting a region as a matching object in a range of a
size ratio equal to or larger than a largest value among values of first
size ratios in the regions of the frame image.

[0166] (8) The photographing system according to (6), further including a
motion detection section performing motion detection based on frame
difference between the plurality of frame images acquired at time points
different from one another, wherein the matching section corrects each of
the first and second size ratios for each of the regions of the frame
image based on a result of the motion detection.

[0167] (9) The photographing system according to (2), wherein the matching
section acquires information on a relevant subject, based on the subject
image, and corrects each of the first and second size ratios based on the
information.

[0168] (10) The photographing system according to (2), wherein the first
size ratio corresponds to a distance between the photographing section
and a subject nearest the photographing section, and the second size
ratio corresponds to a distance between the photographing section and a
subject most distant from the photographing section.

[0169] (11) The photographing system according to any one of (1) to (10),
wherein the matching section changes the size ratio by changing size of
the frame image.

[0170] (12) The photographing system according to any one of (1) to (10),
wherein the matching section changes the size ratio by changing size of
the template image.

[0171] (13) The photographing system according to any one of (1) to (12),
wherein the subject is a face.

[0172] (14) A pattern detection system including

[0173] a matching section changing size of one or both of a frame image
including a subject image and a beforehand prepared template image to
change a size ratio of the template image to the subject image, and
performing pattern matching between the subject image and the template
image, size of one or both of the subject image and the template image
being changed, for each of size ratios,

[0174] wherein the matching section repeats image search through pattern
matching while sequentially changing the size ratio, and obtains one or
more size ratios at which patterns match each other, in a certain order
of image search, and holds, as a first size ratio, a size ratio having a
largest value among such obtained size ratios, and thereafter performs
image search in a manner that pattern matching is performed at a first
frequency in a range of a size ratio equal to or larger than the first
size ratio, and is performed at a frequency lower than the first
frequency in a range of a size ratio smaller than the first size ratio.

[0175] (15) An electronic unit including a photographing system and a
control section performing operation control using the photographing
system, the photographing system including:

[0176] a photographing section photographing a subject to acquire a frame
image including a subject image; and

[0177] a matching section changing size of one or both of the subject
image and a beforehand prepared template image to change a size ratio of
the template image to the subject image, and performing pattern matching
between the subject image and the template image, size of one or both of
the subject image and the template image being changed, for each of size
ratios,

[0178] wherein the matching section repeats image search through pattern
matching while sequentially changing the size ratio, and obtains one or
more size ratios at which patterns match each other, in a certain order
of image search, and holds, as a first size ratio, a size ratio having a
largest value among such obtained size ratios, and thereafter performs
image search in a manner that pattern matching is performed at a first
frequency in a range of a size ratio equal to or larger than the first
size ratio, and performed at a frequency lower than the first frequency
in a range of a size ratio smaller than the first size ratio.

[0179] The present disclosure contains subject matter related to that
disclosed in Japanese Priority Patent Application JP 2011-191036 filed in
the Japan Patent Office on Sep. 1, 2011, the entire content of which is
hereby incorporated by reference.

[0180] It should be understood by those skilled in the art that various
modifications, combinations, sub-combinations and alterations may occur
depending on design requirements and other factors insofar as they are
within the scope of the appended claims or the equivalents thereof.